U.S. patent application number 10/490722 was filed with the patent office on 2005-02-10 for axial flux permanent magnet generator/motor.
Invention is credited to Peeters, Eef, Van Tichelen, Paul.
Application Number | 20050029886 10/490722 |
Document ID | / |
Family ID | 8185032 |
Filed Date | 2005-02-10 |
United States Patent
Application |
20050029886 |
Kind Code |
A1 |
Van Tichelen, Paul ; et
al. |
February 10, 2005 |
Axial flux permanent magnet generator/motor
Abstract
The present invention is related to a permanent magnet
electrical generator/motor comprising a stator, a rotor, a
rotational axis and an air gap between stator and rotor so that the
magnetic flux across said air gap is essentially oriented along
said rotational axis, said rotor preferably comprising a plurality
of permanent magnets to form rotor poles, said generator/motor
being characterised in that said stator comprises a disc (1), and a
plurality of magnetic cores (2), said cores (2) being attached to
said disc (1) by attachment means, said cores comprising coils (6)
wound round the legs of said cores. Furthermore, said machine
comprises means for distributing the flux across the air gap
between rotor and stator. Preferably, this takes on the form of
flux distribution plates (28,29), placed between rotor and
stator.
Inventors: |
Van Tichelen, Paul; (Leuven,
BE) ; Peeters, Eef; (Dessel, BE) |
Correspondence
Address: |
MERCHANT & GOULD PC
P.O. BOX 2903
MINNEAPOLIS
MN
55402-0903
US
|
Family ID: |
8185032 |
Appl. No.: |
10/490722 |
Filed: |
August 26, 2004 |
PCT Filed: |
October 18, 2002 |
PCT NO: |
PCT/BE02/00159 |
Current U.S.
Class: |
310/156.32 ;
310/268 |
Current CPC
Class: |
H02K 21/24 20130101 |
Class at
Publication: |
310/156.32 ;
310/268 |
International
Class: |
H02K 021/12 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 18, 2001 |
EP |
01870222.5 |
Claims
1. A permanent magnet electrical generator/motor comprising a
stator, a rotor, a rotational axis and an air gap between stator
and rotor so that the magnetic flux across said air gap is
essentially oriented along said rotational axis, said rotor
comprising a plurality of locations for placing permanent magnets
(25) or elements of magnetic material to form rotor poles, said
generator/motor comprising a first non-magnetic disc (1), and a
plurality of magnetic cores (2), said cores (2) being attached to
said first disc (1) by attachment means, said cores comprising
coils (6), said generator/motor being characterized in that said
generator/motor further comprises a number of flux distribution
plates in between the stator and the rotor, said plates being made
of magnetic material.
2. A generator/motor according to claim 1, comprising an inner (28)
and an outer (29) flux distribution plate, made of magnetic
material, said plates comprising radial extensions (31,33), the
extensions (31) of the inner plate (28) pointing radially outward
with respect to the machine's rotational axis, and the extensions
(33) of the outer plate (29) pointing radially inward, so that each
extension (31) of said inner plate is adjacent an extension (33) of
said outer plate, with an air gap (34) in between each pair of said
adjacent extensions (31,33).
3. A generator/motor according to claim 2, wherein the edges of
said air gap (34), which are formed by the edges of two adjacent
extensions (31,33) are parallel to each other.
4. A generator motor according to claim 2, wherein said flux
distribution plates (28,29) are attached to the rotor, and wherein
each of said extensions (31,33) covers at least the area of one
permanent magnet location.
5. A generator/motor according to claim 2, wherein said cores (2)
comprise a number of upstanding legs around which said coils (6)
are wound, and wherein said flux distribution plates are attached
to the stator, wherein each of said extensions (31,33) covers at
least the area of the cross section of one leg of a core (2).
6. A generator/motor according to claim 2, wherein the contour of
said extensions (31,33) comprises two straight portions (40), and a
circular portion (41) connecting said two straight portions, so
that two adjacent straight portions of two adjacent extensions
(31,33) are parallel to each other and at an angle to any radius of
said rotor which is crossing said two adjacent straight portions
(40).
7. A generator/motor according to claim 1, wherein said flux
distribution plates comprise adjacent strips of magnetic
material.
8. A generator/rotor according to claim 7, wherein said flux
distribution plates (28,29) comprise cuts (37) through the complete
thickness of the plates, in those parts of the plates which face
the rotor poles.
9. A generator/motor according to claim 1, wherein a separate flux
distribution plate is provided for every rotor pole.
10. A permanent magnet electrical generator/motor comprising a
stator, a rotor, a rotational axis and an air gap between stator
and rotor so that the magnetic flux across said air gap is
essentially oriented along said rotational axis, said rotor
comprising a plurality of locations for placing permanent magnets
(25) or elements of magnetic material to form rotor poles, said
generator/comprising a first non-magnetic disc (1), and a plurality
of magnetic cores (2), said cores (2) being attached to said first
disc (1) by attachment means, said cores comprising coils (6),
characterized in that said locations are shaped so that their
contour parallel to the rotor surface comprises two concentric
circular portions (50) and two connecting portions (51) connecting
the end points of said circular portions (50), wherein two adjacent
connecting portions (51) of two adjacent locations are parallel to
each other.
11. A generator/motor according to claim 1, wherein said means for
attaching said cores (2) to said first disc (1) comprise L-profiles
(3) and bolts (4,5).
12. A generator/motor according to claim 1, further comprising a
ring (27) of magnetic material, connected to the rotor on the side
opposite the stator.
13. A generator/motor according to claim 1, further comprising a
second non-magnetic disc (8), said cores (2) being present between
said first and second disc.
14. A generator/motor according to claim 1, wherein said coils (6)
are attached to said cores by glueing.
15. A generator/motor according to claim 1, further comprising a
second stator, which is placed opposite the first stator on the
other side of said rotor,
16. A generator/motor according to claim 15, wherein said second
stator is rotated over an angle around the rotational axis of said
generator/motor, with respect to said first stator.
17. A generator/motor according to claim 1, further comprising at
least one electronic converter, which works in "boost-mode" at low
speed and as a rectifier at high speed.
18. A generator/motor according to claim 1, wherein the rotor
comprises in every one of said locations, a permanent magnet.
19. A generator/motor according to claim 1, wherein the rotor
comprises in said locations a number of permanent magnets and a
number of elements made of magnetic material.
20. A generator/motor according to claim 1, wherein the rotor
comprises only elements made of magnetic material and placed into
said permanent magnet locations, in such a way that the number of
rotor poles is different from the number of stator poles.
21. A generator/motor according to claim 1, wherein said cores (2)
are U-shaped cores or E-shaped cores.
22. A generator/motor according to claim 1, further comprising a
ring (52) made of laminated magnetic material, said ring connecting
the cores (2) of said stator.
Description
FIELD OF THE INVENTION
[0001] The present invention is related to an axial flux permanent
magnet generator/motor, for example for use with internal
combustion engines, where this type of machine is incorporated in
the flywheel.
STATE OF THE ART
[0002] The axial flux permanent magnet generator and motor has been
described in various forms. It consists of a stator comprising a
plurality of coils, and a rotor comprising several permanent
magnets, wherein an air gap is present between stator and rotor.
The notion of `axial flux` is not always defined in the same way.
In this text, the expression `axial flux` is related to machines
wherein the flux across the air gap is essentially parallel to the
machine's rotational axis.
[0003] The closest prior art when it comes to this type of machine
has been disclosed in the publication entitled `An Axial Flux
Interior PM Synchronous Machine`, by D. H. Kang et al., ICEM 2000,
28-30 Aug. 2000. It comprises two stators, each made as a single
hollow cylinder with radial slots cut out of one of the ring-shaped
surfaces. The coils are then wound round the radial extensions left
in between the removed slots. The manufacture of such a stator is
complex as well as expensive, especially in small series.
AIMS OF THE INVENTION
[0004] The present invention aims to provide a new axial flux
permanent magnet generator/motor, with reduced complexity and cost
compared to the prior art, whilst presenting solutions for problems
intrinsic in the simplified design according to the invention.
SUMMARY OF THE INVENTION
[0005] The present invention is related to a permanent magnet
electrical generator/motor comprising a stator, a rotor, a
rotational axis and an air gap between stator and rotor so that the
magnetic flux across said air gap is essentially oriented along
said rotational axis, said rotor comprising a plurality of
locations for placing permanent magnets or elements of magnetic
material to form rotor poles, said generator/motor comprising a
first non-magnetic disc and a plurality of magnetic cores, said
cores being attached to said first disc by attachment means, said
cores comprising coils, said generator/motor being characterized in
that it further comprises a number of flux distribution plates in
between the stator and the rotor, said plates being made of
magnetic material.
[0006] These flux distribution plates may be in the form of a
separate plate placed before each pole. Alternatively, these flux
distribution plates may be designed as an inner and an outer flux
distribution plate, made of magnetic material, said plates being
present in between the stator and the rotor, said plates comprising
radial extensions, the extensions of the inner plate pointing
radially outward with respect to the machine's rotational axis, and
the extensions of the outer plate pointing radially inward, so that
each extension of said inner plate is adjacent an extension of said
outer plate, with an air gap in between each pair of said adjacent
extensions. The edges of said air gap, which are formed by the
edges of two adjacent extensions are preferably parallel to each
other.
[0007] The flux distribution plates may be attached to the rotor,
so that each of said extensions covers at least the area of one
permanent magnet location.
[0008] Alternatively, the flux distribution plates may be attached
to the stator, so that each of said extensions covers at least the
area of the cross section of one leg of a core.
[0009] According to one embodiment, the contour of said extensions
comprises two straight portions, and a circular portion connecting
said two straight portions, so that two adjacent straight portions
of two adjacent extensions are parallel to each other and at an
angle to any radius of said rotor which is crossing said two
adjacent straight portions.
[0010] Flux distribution plates according to the invention may
comprise adjacent strips of magnetic material. According to the
preferred embodiment, said flux distribution plates comprise cuts
through the complete thickness of the plates, in those parts of the
plates which face the rotor poles.
[0011] The invention is equally related to a permanent magnet
electrical generator/motor comprising a stator, a rotor, a
rotational axis and an air gap between stator and rotor so that the
magnetic flux across said air gap is essentially oriented along
said rotational axis, said rotor comprising a plurality of
locations for placing permanent magnets or elements of magnetic
material to form rotor poles, said generator/motor comprising a
first non-magnetic disc and a plurality of magnetic cores, said
cores being attached to said first disc by attachment means, said
cores comprising coils, said generator/motor being characterized in
that the rotor comprises locations which are shaped so that their
contour parallel to the rotor surface comprises two concentric
circular portions and two connecting portions connecting the end
points of said circular portions, wherein two adjacent connecting
portions of two adjacent magnets are parallel to each other.
[0012] Said means for attaching said cores to said first disc may
comprise L-profiles and bolts.
[0013] A generator/motor according to the invention may further
comprise a ring of magnetic material, connected to the rotor on the
side opposite the stator. This ring may also be made of laminated
magnetic material.
[0014] According to one embodiment, the generator/motor according
to the invention further comprises a second non-magnetic disc, said
cores being present between said first and second disc. According
to another embodiment, said coils are attached to said cores by
glueing.
[0015] A generator/motor according to the invention may further
comprise a second stator, which is placed opposite the first stator
on the other side of said rotor. Said second stator may be rotated
over an angle around the rotational axis of said generator/motor,
with respect to said first stator.
[0016] A generator/motor according to the invention may further
comprise at least one electronic converter, which works in
"boost-mode" at low speed and as a rectifier at high speed.
[0017] The rotor may comprise in every one of said locations a
permanent magnet. Alternatively, the rotor may comprise a number of
permanent magnets and a number of elements made of magnetic
material.
[0018] In another design according to the invention, the rotor may
comprise only elements made of magnetic material and placed into
said permanent magnet locations, in such a way that the number of
rotor poles is different from the number of stator poles.
[0019] The cores which are used on the stator may be U-shaped cores
or E-shaped cores.
[0020] In the case of 3 or more phase machine, the generator/motor
according to the invention preferably further comprises a ring made
of laminated magnetic material, said ring connecting the cores of
said stator.
SHORT DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 shows a photograph of a partly assembled stator
according to the invention.
[0022] FIG. 2 shows a photograph of a complete rotor according to
the invention.
[0023] FIGS. 3a and 3b represent overviews of an axial flux
generator/motor according to the invention.
[0024] FIG. 4 represents a first sectional view of the stator of
the invention, as shown in FIG. 3a.
[0025] FIG. 5 represents a second sectional view of the stator of
the invention, as shown in FIG. 3a.
[0026] FIG. 6 represents a sectional view of the rotor of the
invention, as shown in FIG. 3.
[0027] FIG. 7 represents a view of a rotor according to a second
embodiment of the invention.
[0028] FIG. 8 represents a view of a pair of flux distribution
plates, which comprise cuts.
[0029] FIG. 9 represents a view of a ring of laminated magnetic
material, which can be installed on the stator in case of a 3 or
more phase machine.
[0030] FIG. 10 illustrates the rotation of one stator with respect
to the other, in the embodiment of the invention comprising two
stators.
DETAILED DESCRIPTION OF THE INVENTION
[0031] The present invention generally presents a concept for an
axial flux permanent magnet generator/motor, wherein a number of
cores 2 are attached onto a disc 1, in order to form the stator.
The disc 1 is preferably circular shaped, but the function of this
disc can be performed by any plate made of a non-magnetic material.
Also, the disc or plate 1 may be made of a magnetic material, which
is covered by an insulation. The photograph of FIG. 1 illustrates a
partly assembled stator according to the invention, comprising six
U-cores. The fact that separate cores are used allows the use of
standard cores, thus leading to a straightforward and inexpensive
design.
[0032] The main problem of using such a design however, resides in
the large fluctuation of the air gap between such a stator and the
rotor, which is to be placed facing the cores on the stator. The
rotor will preferably comprise a number of permanent magnets of a
given form, at equal distances on a circle which is co-axial with
respect to the machine's rotational axis. The large air gap
fluctuation is then being caused by the large open spaces left
in-between adjacent cores 2 on the disc 1, as well as in between
the legs of one core 2, making the changeover between two adjacent
poles difficult. The present invention solves this problem by
providing an extra feature in the form of means for distributing
the flux in an optimal way across the whole of the air gap's cross
section perpendicular to the machine's rotational axis.
[0033] In order to do this, and according to the preferred
embodiment, the rotor or the stator are equipped with so-called
`flux-distribution plates`, which are specially shaped plates made
of magnetic material, placed in the path of the axial flux between
rotor and stator, and which allow the change-over fluctuation to be
reduced to a minimum. A possible shape of these plates 28, 29 when
attached to the rotor, are illustrated in FIG. 2.
[0034] According to a further embodiment, the feature of flux
distribution is obtained by shaping the permanent magnets
themselves in a pre-defined way.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
[0035] A preferred embodiment of the machine of the invention is
shown in detail in FIG. 3a. It concerns a mono-phase disc permanent
magnet generator, equipped with twelve cylinder-shaped permanent
magnets 25 and flux-distribution plates 28,29 on the rotor.
Sectional views indicated in FIG. 3 are shown in subsequent FIGS. 4
to 6. The stator comprises a disc 1, made of non-magnetic material,
onto which six magnetic cores 2 are attached. These are U-shaped
cores and can be any type of standard core, made of laminated
magnetic material. They are attached to the disc 1 by a number of
L-shaped profiles 3, bolted onto the disc 1 by bolts 4 and onto the
cores 2 by bolts 5. The cores 2 are attached in such a way that the
upstanding legs are essentially perpendicular to the disc 1.
[0036] The coils 6 are preferably wound round coil formers 7, which
are then placed on the upstanding legs of the cores 2. A second
non-magnetic disc 8 is preferably added opposite the first disc 1,
so that both discs take care of the clamping of the cores with
sufficient strength and of the jamming of the coils in the cores.
Rectangular openings are present in the second disc 8 corresponding
to the top surfaces 9 of the legs of the U-shaped cores.
[0037] The first and second disc (1,8) are held together by a set
of bolts 20, in combination with tubes 21. This assembly is then
attached through an additional set of bolts 23 and tubes 24 to a
stationary plate 22, which represents the structure onto which the
machine is installed.
[0038] The rotor is positioned in between this stationary plate 22
and the second disc 8. This rotor comprises a number of permanent
magnets 25 with alternated orientation of north and south poles.
The permanent magnets are cylinder-shaped. Standard magnets of this
type may be used, such as loudspeaker magnets. The magnets are
clamped into a non-magnetic circular disc 26.
[0039] At the back of this non-magnetic disc 26, the permanent
magnets are connected by a ring 27 of magnetic material, in order
to create a magnetic path. On the surface directly facing the
stator, the rotor is equipped with two flux distribution plates 28
and 29. These are best illustrated in FIG. 6 and on the photograph
of FIG. 2. In FIG. 6, the magnets 25 are made visible, for
clarity's sake. The flux distribution plates are made of magnetic
material. Each plate is essentially a ring-shaped disc with radial
extensions covering one type (north or south) of magnetic pole. The
inner plate 28 is attached by bolts 30 to the rotor disc 26 and
comprises radial extensions 31, which are pointing outward from the
central ring into which the bolts 30 are present. Each of these
extensions 31 covers the complete area of one type of permanent
magnet. The outer plate 29 is equally bolted by bolts 32 to the
rotor disc 26, and comprises radial extensions 33 which are
pointing inward from the circumferential ring where the bolts 32
are present. The extensions 33 are covering the area of the
remaining magnets, in between the magnets which are already covered
by the inner plate 28. The surface of the extensions 31,33 is
preferably larger than the surface of the magnets which they
cover.
[0040] The specific contour of the extensions in this preferred
embodiment can be seen to comprise two straight portions 40 and a
circular portion 41, essentially concentric with the rotor. The
straight portions 40 are not oriented along a radius of the rotor,
but are at an angle to any rotor radius crossing said straight
portions. As a consequence, the air gap 34 between two adjacent
extensions is at an angle to the rotor radius. The reason for this
is explained after this.
[0041] Every extension 31 of the inner plate 28 is adjacent an
extension 33 of the outer plate 29. The air gap 34 between these
flux distribution plates is larger than the air gap between the
flux distribution plates and the magnetic material of the stator,
in order to avoid flux lines crossing the air gap between flux
distribution plates.
[0042] The function of these flux distribution plates is to
mitigate the effect of the large fluctuation in air gap volume, as
a consequence of the use of separate U-cores on the stator, which
might otherwise lead to the problem of torque pulsation (cogging).
For this purpose, the area of the extensions 31,33 is as large as
possible, with the limitation that the air gap 34 between adjacent
extensions needs to be larger than the air gap between rotor and
stator. Furthermore, the air gap 34 between the flux distribution
plates 28 and 29 is designed at an angle to the radius of the
rotor, as a further measure against torque pulsation. This way, the
changeover between two poles with different orientation can take
place with a minimal variation in air gap volume between the flux
distribution plates and the magnetic material of the stator.
[0043] The rotor disc is attached to a central part 35, which is to
be connected to the machine axis. The connection between this
central part and the rotor disc is supplied by bolts 36.
ALTERNATIVE EMBODIMENTS OF THE INVENTION
[0044] FIG. 3b shows a slightly modified embodiment which is
essentially equivalent to the one shown in FIG. 3a, and wherein the
second disc 8 has been omitted, along with the bolts 20 and tubes
21. In this embodiment, the clamping of the coils onto the cores is
done by other attaching means, preferably by glueing the coils 6 to
the cores 2.
[0045] The flux distribution plates may be attached to the stator,
facing the rotor, instead of to the rotor. The same form of plates
may be used in this case. The effect obtained by these plates, put
onto the stator is exactly the same as in the above described case.
Each extension 31 or 33 of one of both plates then covers at least
the area of the cross-section of one leg of a core 2.
[0046] The form of flux distribution plates is not limited to the
one shown in the figures. The main characteristic of such a plate
is that it essentially covers at least the area of one rotor or
stator pole. It is also possible to provide a separate flux
distribution plate for every rotor pole.
[0047] The magnet arrangement is not necessarily based on a series
of alternating north and south-oriented permanent magnets, but may
also be based on groups of north-oriented magnets adjacent to
groups of south-oriented magnets. This is the preferred case for
example in a 3 or more phase machine according to the invention.
One rotor pole then comprises a group of similarly oriented
magnets. In this case therefore, flux distribution plates installed
on the rotor may have fewer but larger extensions 31,33 which cover
such a group of adjacent magnets of the same orientation.
Alternatively, separate flux distribution plates may be installed,
each covering one rotor pole.
[0048] The flux may also be distributed in the same way by shaping
the permanent magnets themselves in a given way. This effect is
obtained by using magnets which have the shape of the radial
extensions (31,33) of the flux distribution plates 28 and 29. A
rotor of this kind, equipped with specially shaped magnets 45 is
shown in FIG. 7. These magnets are then equally clamped into a
non-magnetic disc 26. No flux distribution plates are required in
this embodiment. The magnets of FIG. 7 have two concentric circular
portions 50 and two connecting portions 51 between the end points
of said circular portions. In this case, the connecting portions 51
are straight lines, which are not parallel to the rotor radius, in
order to avoid torque pulsation.
[0049] For both the latter embodiment, as the one with flux
distribution plates, it is not required that the adjacent edges of
the extensions 31,33 or of the magnets 45 are straight lines. These
edges may have any shape. It is however preferred that adjacent
edges are parallel.
[0050] In order to adapt it to a 3 or more phase machine, the rotor
of FIG. 7 may also comprise a smaller number of larger magnets 45,
equally comprising portions 50, 51 but each taking up a larger
space in the rotor's circumference.
[0051] Instead of U-shaped cores, E-shaped cores may be used.
[0052] In the machine shown in FIG. 3, it is not necessary to use
permanent magnets in every position 25. It is also possible to have
a rotor wherein every second position is filled by a permanent
magnet. This may be a solid permanent magnet or a permanent magnet
made of laminated material. For example, all magnets having their
north pole at the left in FIG. 3 may be replaced by a disc made of
magnetic material, preferably laminated magnetic material. Because
it is not required to have permanent magnets at every position 25
around the rotor, as shown in FIG. 6, these positions may more
generally be called `locations`, to be filled in either by
permanent magnets or_by elements of laminated magnetic material of
the same or other shape as the permanent magnets.
[0053] The ring 27 at the back of the rotor is preferably formed of
a laminated material.
[0054] To limit the magnetic losses in the flux distribution plates
28,29 these plates or at least part of these plates preferably
comprise `interruptions` perpendicular to the plate's plane
surface. In general, the plate may be said to comprise a series of
adjacent strips of magnetic material, lying next to each other, and
thereby making up the plate or a part of the plate.
[0055] In the preferred embodiment, the plates are machined, for
example by a laser tool, in order to form cuts 37 which go through
the complete thickness of the plates and which are located at least
in those parts of the plate facing the rotor poles, see FIG. 8.
Parts on either side of such a cut 37 are understood to be the
`adjacent strips` in the more general description.
[0056] In a special design for the 3 or more phase machines the
magnetic cores of the stator can be magnetically combined by
layered rings of magnetic material. FIG. 9 shows such a layered
ring 52, comprising open spaces 53 which are to be placed over the
cores 2 on the stator. The ring 52 is then placed in between the
disc 1 and the coil formers 7.
[0057] For the 3 or more phase system, a special rotor construction
can be made so that the machine works as a switched reluctance
motor or generator without the use of permanent magnets on the
rotor. All of the rotor poles can then be built by elements of
magnetic material, preferably laminated, with a special design
resembling the radial extensions 31, 33 in order to produce the
same effect as with the flux distribution plates, or by preferably
laminated magnetic elements, equipped with flux distribution plates
as described above. For the switched reluctance machine the pole
number of the rotor differs from the pole number of the stator. The
equilibrium position of the rotor (minimal reluctance) turns with
the alternate excitation of the different stator poles.
[0058] It is also possible to make a twin type of machine by
replacing the stator construction at the front of the rotor by two
similar stator constructions one at each side of the rotor. For
this design, the rotor does not need the magnetic ring 27 at the
backside since the magnetic path is already closed at each side of
the rotor by the magnetic cores of the stator. The flux
distribution plates 28,29 however or the special design of the
permanent magnets have to be present at both sides of the rotor for
this construction. According to the preferred embodiment, the
stators are rotated over an angle with respect to each other,
around the rotational axis, as is illustrated in FIG. 10. This is
preferred in order to reduce torque pulsations.
[0059] The machine can only generate a controlled output voltage if
an electronic converter is being used. The converter works in
"boost-mode" at low speed and as a rectifier at high speed. For the
3-phase construction, the electronic converter has the additional
function of motor control when the machine is used as a motor.
[0060] It is possible to generate a 3-phase output with the 1-phase
construction by using 3 electronic converters each on a 1-phase
output.
[0061] To reduce the weight of the machine, it is possible to make
the coils 6 of the stator with aluminium foil instead of with
copper wire.
* * * * *